This invention is generally related to color printing, and more particularly, to a method of printing a fluorescent image superimposed on a color image such that only an outline of the color image fluoresces to enhance visibility of the image when the image is viewed in a dark viewing area.
Printers, such as thermal dye color printers and ink jet color printers, print color images supplied by an image source, such as a camera. The image source in turn transmits the image as an image file to a controller that controls operation of a print head. The print head then operates to print the image on a receiver according to the image file transmitted to the controller.
More specifically, thermal dye color printers thermally activate a dye carrier having a repeating series of spaced frames of different colored heat transferable dyes. In such printers, the carrier is disposed between the receiver, such as coated paper, and a plurality of individual heating elements of a printhead. When a particular heating element is energized, dye transfers from the carrier to the receiver. The density of the printed colored dye image is a function of the energy delivered by the heating element to the carrier. Thermal dye transfer printers offer the advantage of true xe2x80x9ccontinuous tonexe2x80x9d dye density transfer by varying the energy applied to each heating element, thereby yielding variable dye density image pixels on the receiver.
The dye frames of the carrier are typically yellow, magenta and cyan dye frames. First, as the yellow dye frame and the receiver are simultaneously advanced and positioned under the print head, the heating elements are selectively energized corresponding to the blue information of the input image data in order to form a row of yellow image pixels in the receiver. This process is repeated until a yellow dye image is formed in the receiver. The receiver is then retracted the same distance as it was advanced. Next, the magenta dye frame and the receiver are simultaneously advanced and positioned under the print head and the heating elements are again selectively energized corresponding to the green information of the input image data in order to form a magenta image superimposed upon the yellow image. The receiver is again retracted the same distance as it was advanced. Finally, the cyan dye frame and the receiver are simultaneously advanced and positioned under the print head and the heating elements are selectively energized corresponding to the red information of the input image data to form a cyan dye image superimposed upon the yellow and magenta dye images. The yellow, magenta and cyan dye images combine to form a color image. In some printers, a lamination dye layer (i.e., a transparent dye layer) is transferred to the receiver over the color image to protect the image from damage. This protective dye layer preferably has a uniform thickness and is transferred to the receiver by energizing all the heating elements with a uniform energy level.
In another method of thermal printing, one or all of the colored dye frames may contain phosphorous pigments. The image printed with such a dye frame is indistinguishable with an image printed with ordinary dye when viewed under a broad spectrum light, but with fluorescence the image becomes visible in a dark viewing area. In this manner, the printer produces a xe2x80x9cglow in the darkxe2x80x9d print.
However, thermal dye printers that use phosphorous pigments mixed with the color dyes to produce the glow in the dark print have several drawbacks. For example, since typical image data of a color plane contains varying density of information, from minimum density to maximum density, and is typically dispersed throughout the color plane, the resulting print fluoresces substantially uniformly. Hence, when such a print is viewed in a dark area, the whole printed area glows, making the image virtually unrecognizable.
In the case of an ink jet printer, digital signals as to each of four colors (i.e., red, green, blue and black) regarding an image are processed in a manner so that a multi-nozzle print head belonging to the ink jet printer forms a printed color image on the receiver. More specifically, when the sidewalls of corresponding ink channels formed in the print head inwardly move due to actuation of the sidewalls, a pressure wave is established in the ink contained in the channel. This pressure wave squeezes a portion of the ink in the form of an ink droplet out the ink channel. This ink droplet lands on the receiver to form a pixel. A multiplicity of such pixels form the image.
However, as in the case of thermal dye printing, one or all of the colored inks may contain phosphorous pigments. The image printed with such an ink is indistinguishable with an image printed with ordinary ink when viewed under a broad spectrum light, but with fluorescence the image becomes visible in a dark viewing area. In this manner, ink jet printers can also produce a xe2x80x9cglow in the darkxe2x80x9d prints.
However, ink jet printers that use phosphorous pigments mixed with color ink have several drawbacks. For example, since typical image data of a color plane contains a varying density of information, from minimum density to maximum density, and is typically dispersed throughout the color plane, the resulting print fluoresces substantially uniformly. Hence, when such a print is viewed in a dark area, the whole printed area glows, making the image virtually unrecognizable.
Therefore, there is a need to provide a method of printing a fluorescent image superimposed on a color image such that the image is recognizable when the image is viewed in a dark viewing area.
The present invention provides a xe2x80x9cglow in the darkxe2x80x9d image by utilizing an additional phosphorous color plane to transfer phosphorous pigments. First, the yellow dye frame and the receiver are moved to be positioned under the print head and as they are advanced, the heating elements are selectively energized corresponding to the blue information of the input image data to form a row of yellow image pixels in the receiver. This process is repeated until a yellow dye image is formed in the receiver. The receiver is then retracted the same distance as it was advanced. Next the magenta dye frame is moved under the print head and the receiver is also moved under the print head. Both the receiver and the magenta dye frame are advanced as the heating elements are selectively energized corresponding to the green information of the input image data and a magenta image is formed superimposed upon the yellow image. The receiver is again retracted the same distance as it was advanced. The cyan dye frame and the receiver are moved under the print head. Both the receiver and the cyan dye frame are advanced as the heating elements are selectively energized corresponding to the red information of the input image data and a cyan dye image is formed on the receiver superimposed upon the yellow and magenta dye images. A phosphorus color plane is then transferred to the receiver. The phosphorous color plane is preferably derived from the green color plane and contains only bi-modal edge information of the image in the green color plane. All other information of the green color plane is discarded.
Thus, phosphorous pigments are transferred and superimposed to the color image only to outline the original image with the edge information. The resulting print produces a well-defined glow in the dark image when the print is viewed in a dark area because only the outline of the image fluoresces.
It is an object of the present invention to provide a method of printing a fluorescent image that when viewed in a dark area produces a sharp image.
It is another object of the present invention to provide a method of printing an image which in ambient light shows a non-fluorescent image and in a dark area shows a sharp fluorescent image.
It is a further object of the present invention to provide a method which produces a sharp fluorescent image using standard, commercially available, thermal dye printers or ink jet printers.
A feature of the present invention is the provision of a dye donor ribbon having a phosphorous color patch that is used to produce a phosphorescent image preferably derived from the green color plane of a color image, the phosphorescent image containing only bi-modal edge information of the green color plane.
An advantage of the present invention is that use thereof provides a glow in the dark print having an image that is recognizable when viewed in a dark area.
Other objects, features and advantages of the present invention will be apparent from the following detailed description in which the preferred embodiments have been set forth in conjunction with the accompanying drawings.